1. Field of the Invention
The present invention relates generally to a Visible Light Communication (VLC) system, and more particularly, to a method and device for determining an output of a visible frame according to a communication environment in a VLC system.
2. Description of the Related Art
With improved luminous efficiency and competitive price, Light Emitting Diodes (LEDs) are more often used in special lighting markets for mobile devices, displays, vehicles, traffic lights, advertising boards, etc., and also in general light markets for fluorescent lamps, incandescent lamps, etc. Further, due to the exhaustion of Radio Frequency (RF) band frequencies, the possibility of a conflict between various wireless communication techniques, the increased demand for communication security, the advent of ubiquitous super-high speed communication environments in a 4th Generation (4G) wireless technology, etc., there is a growing interest in an optical wireless technology complementary to an RF technology, such as VLC using LEDs.
VLC that transmits information using visible light is safe, wide in bandwidth, and free for use. In addition, VLC enables a user to accurately perceive an information reception range because the user can see a light arrival place or a light traveling direction. Accordingly, VLC is reliable in terms of security and can be driven with lower power. VLC may be applied even in hospitals and airplanes where the use of RF is limited and may provide additional information services using an electronic signboard.
FIG. 1 illustrates a conventional VLC system.
Referring to FIG. 1, the conventional VLC system includes a light source 10 and a VLC terminal 20. The light source 10, which includes LEDs or Laser Diodes (LDs), transmits and receives data using visible light. The VLC terminal 20 includes a visible light transmission/reception module for transmitting and receiving data to and from the light source 10. The VLC terminal 20 may be a mobile terminal, such as a cellular phone or a Personal Digital Assistant (PDA), or a fixed terminal such as a desktop type.
Generally, a plurality of light sources 10 are installed for VLC. When the plurality of light sources are installed at regular intervals, multiple service areas provided by the light sources.
FIGS. 2 to 4 illustrate examples of service areas provided by two light sources.
As illustrated in FIG. 2, service areas provided by light sources 30 and 40 may overlap each other.
As illustrated in FIG. 3, service areas provided by the light sources 30 and 40 may contact each other at their boundaries.
As illustrated in FIG. 4, service areas provided by the light sources 30 and 40 may be separated from each other so that a non-service area is present.
Among the examples illustrated in FIGS. 2-4, FIG. 3 illustrates an ideal state, which is difficult to achieve in reality. Generally, service areas provided by a plurality of light sources include an overlap area, as illustrated in FIG. 2, or include a non-service area, as illustrated in FIG. 4.
When providing a unicast, multicast, or broadcast communication service to multiple user terminals using VLC, the multiple user terminals may be located in a service area provided by one light source and each terminal may receive the same or individual data. Because VLC uses visible light, the transmission and reception of data can be easily performed when communication links of a transmitter and a receiver are aligned in both directions. Even in one-way communication, the communication links should be formed to accurately direct a visible light signal generated from a visible light transmitting part of the transmitter to a visible light receiving part of the receiver. Consequently, communication links for terminals that receive data from a light source are often disconnected or a visible light signal is not properly transmitted, due to external environment factors, movement of terminals, obstacles in the communication paths, etc. Even when there are a plurality of terminals that receive data from one light source, communication links may be disconnected from one of the multiple terminals.
Therefore, a need exists for a method for determining an output of a visible frame in consideration of various communication environments using VLC terminals.
A need also exists for a method for determining an output of a visible frame in consideration of a data non-transmission interval, misalignment, a Negative ACKnowledgement (NACK) signal, user selection, etc.